The Impact and Recovery of Asteroid 2008 TC3 P
Total Page:16
File Type:pdf, Size:1020Kb
Vol 458 | 26 March 2009 | doi:10.1038/nature07920 LETTERS The impact and recovery of asteroid 2008 TC3 P. Jenniskens1, M. H. Shaddad2, D. Numan2, S. Elsir3, A. M. Kudoda2, M. E. Zolensky4,L.Le4,5, G. A. Robinson4,5, J. M. Friedrich6,7, D. Rumble8, A. Steele8, S. R. Chesley9, A. Fitzsimmons10, S. Duddy10, H. H. Hsieh10, G. Ramsay11, P. G. Brown12, W. N. Edwards12, E. Tagliaferri13, M. B. Boslough14, R. E. Spalding14, R. Dantowitz15, M. Kozubal15, P. Pravec16, J. Borovicka16, Z. Charvat17, J. Vaubaillon18, J. Kuiper19, J. Albers1, J. L. Bishop1, R. L. Mancinelli1, S. A. Sandford20, S. N. Milam20, M. Nuevo20 & S. P. Worden20 In the absence of a firm link between individual meteorites and magnitude H 5 30.9 6 0.1 (using a phase angle slope parameter their asteroidal parent bodies, asteroids are typically characterized G 5 0.15). This is a measure of the asteroid’s size. only by their light reflection properties, and grouped accordingly Eyewitnesses in Wadi Halfa and at Station 6 (a train station between into classes1–3. On 6 October 2008, a small asteroid was discovered Wadi Halfa and Al Khurtum, Sudan) in the Nubian Desert described a with a flat reflectance spectrum in the 554–995 nm wavelength rocket-like fireball with an abrupt ending. Sensors aboard US govern- range, and designated 2008 TC3 (refs 4–6). It subsequently hit the ment satellites first detected the bolide at 65 km altitude at Earth. Because it exploded at 37 km altitude, no macroscopic 02:45:40 UTC (ref. 8). The optical signal consisted of three peaks span- fragments were expected to survive. Here we report that a dedicated ning 3.5 s, with most of the radiated energy in the middle 1-s pulse at search along the approach trajectory recovered 47 meteorites, an inferred altitude of about 37 km, and a final pulse 1 s later. Meteosat fragments of a single body named Almahata Sitta, with a total mass 8 (ref. 9) detected the brightest optical signal when the asteroid was at of 3.95 kg. Analysis of one of these meteorites shows it to be an 37.5 6 1.0 km. Rapidly fading infrared radiation was detectable down achondrite, a polymict ureilite, anomalous in its class: ultra-fine- until at least 32.7 6 0.7 km. The 10-mm Si–O band of glowing dust was grained and porous, with large carbonaceous grains. The combined the dominant feature in a seven-channel 6–13 mm infrared spectrum asteroid and meteorite reflectance spectra identify the asteroid as taken ,1 s after the explosion. The height of the dust cloud was F class3, now firmly linked to dark carbon-rich anomalous ureilites, 35.7 6 0.7 km. Independently, we measured this altitude at 35– a material so fragile it was not previously represented in meteorite 42 km, with no significant dust deposition below 33 km, based on collections. UK Meteorological Office10 wind model data and ground-based The asteroid was discovered by the automated Catalina Sky Survey images of the lingering train11 taken from Wadi Halfa at sunrise telescope at Mount Lemmon, Arizona on October 6 06:39 UTC (ref. 4). (03:22–03:27 UTC). Early orbital solutions showed an impact 19 h after discovery with a Unexpectedly, some meteorites survived the explosion. Fifteen predicted impact location in the Nubian Desert of northern Sudan5,6 fresh-looking meteorites with a total mass of 563 g were recovered (Table 1). Numerous astronomical observatories imaged the object by 45 students and staff of the University of Khartoum during a field until it entered the Earth’s umbra on October 7 01:49 UTC.Inthe campaign on 5–8 December 2008. A second search on 25–30 previous two hours, its brightness oscillated with an amplitude of December (72 participants) raised the total to 47 meteorites and 1.02 mag at main periods of 49.0338 6 0.0007 s and 96.987 6 0.003 s, 3.95 kg. Masses range from 1.5 g to 283 g, spread for 29 km along and their harmonics, revealing that the asteroid was in a non-principal- the approach path in a manner expected for debris from 2008 TC3 axis rotation state7. The oscillation was centred on absolute visible (Fig. 1). Nearly all recovered meteorites show a broken face with no corres- Table 1 | Orbital parameters of 2008 TC used to calculate the approach 3 ponding pieces nearby (Fig. 2). One intact fully crusted meteorite was path perfectly oriented in flight, with only a single side exposed to the Symbol Parameter Value oncoming air stream and one rotational degree of freedom (Fig. 2e), a Semimajor axis 1.308201 6 0.000009 AU suggesting that this secondary fragmentation was caused by centri- q Perihelion distance 0.899957 0.000002 AU 6 fugal forces or uneven dynamic pressure from rapid tumbling. v Argument of perihelion 234.44897 6 0.00008u V Longitude of ascending node 194.101138 6 0.000002u Almahata Sitta is a fine-grained fragmental breccia. A small 1.5 g i Inclination 2.54220 6 0.00004u meteorite (no. 7) was broken under 35 lb peak pressure to create a 2008 20 3989 0 0001 Tp Perihelion time November . 6 . UT fresh surface for analysis—all results reported here are from this These parameters are JPL solution 15; equinox J2000, 2008 October 07.0 TDB or Barycentric meteorite. It had a tensile strength of only 56 6 26 MPa, cracking Dynamical Time. The astrometric position of 295 observations were used. This ephemeris, when projected to an altitude of 50 km, predicts an entry velocity of 12.42 km s21 at a shallow along a white layer, rich in pyroxene, sprinkled with darker areas rich 20u angle relative to the surface, with a perpendicular uncertainty in position of only 6100 m. in carbonaceous matter (Fig. 2a). 1SETI Institute, Carl Sagan Center, 515 North Whisman Road, Mountain View, California 94043, USA. 2Physics Department, University of Khartoum, PO Box 321, Khartoum 11115, Sudan. 3Physics Department, Juba University, Juba, Sudan. 4NASA Johnson Space Center, Mail Code KT, Houston, Texas 77058, USA. 5Jacobs Technologies Engineering Science Contact Group (ESCG), Johnson Space Center, Houston, Texas 77058, USA. 6Department of Chemistry, Fordham University, 441 East Fordham Road, Bronx, New York 10458, USA. 7Department of Earth and Planetary Sciences, American Museum of Natural History, 79th Street at Central Park West, New York, New York 10024, USA. 8Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington DC 20015-1305, USA. 9Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA. 10School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK. 11Armagh Observatory, College Hill, Armagh BT61 9DG, UK. 12Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada. 13ET Space Systems, 5990 Worth Way, Camarillo, California 93012, USA. 14Sandia National Laboratories, PO Box 5800, Albuquerque, New Mexico 87185, USA. 15Clay Center Observatory, Dexter and Southfield Schools, 20 Newton Street, Brookline, Massachusetts 02445, USA. 16Astronomical Institute of the Academy of Sciences, Fricˇova 298, 25165 Ondrˇejov Observatory, Czech Republic. 17Czech Hydrometeorological Institute, Na Sabatce 17, 143 06 Praha 4, Czech Republic. 18Institut de Me´canique Ce´leste et de Calcul des E´phe´me´rides, 77 avenue Denfert-Rochereau, 75014 Paris, France. 19Dutch Meteor Society, Akker 141, 3732 XD De Bilt, The Netherlands. 20NASA Ames Research Center, Mail Stop 245-6, Moffett Field, California 94035, USA. 485 ©2009 Macmillan Publishers Limited. All rights reserved LETTERS NATURE | Vol 458 | 26 March 2009 Figure 1 | Map of the Nubian Desert of northern Sudan with the ground- fragments would have stopped ablating at around 32 km altitude, falling projected approach path of the asteroid and the location of the recovered vertically on the ground at 30–60 m s21. Labels in white rectangles mark the meteorites. 2008 TC3 moved from a geodetic longitude of 31.80381u E and position where meteorites of indicated masses are predicted to have fallen latitude of 120.85787u N at 50 km altitude, to 32.58481u E, 120.70569u Nat (calculations assume spheres released at 12.4 km s21 from detonation at 20 km altitude above the WGS-84 ellipsoid. White arrow represents the path 37 km altitude, white star). In light yellow is shown the area that was of the 2008 TC3 fireball with the projected, non-decelerating ground path systematically searched. Special attention was given to possible large represented as a thin black line (altitude labels in km, within white ovals). fragments further down track, but none were found. Such larger masses The sizes of the red symbols indicate small (1–10 g), medium (10–100 g) and would have carried residual forward velocity. The yellow line marks the path large (100–1,000 g) meteorites. Our dark-flight calculations show that 270-g of the local train tracks with the location of Station 6 labelled. Classification of the meteorite was based on oxygen isotopes, bulk of the material being a residue of partial melting13,14. The relatively chemistry, and mineralogy. The oxygen isotope abundance of two high ($0.1 CI) REE abundances in Almahata Sitta are consistent with fragments was measured as: D17O 520.147% and 20.501%, it being a polymict ureilite, which as a group have higher REE con- d17O 5 3.90% and 3.56%, and d18O 5 7.70% and 7.72% relative centrations than the more common monomict ureilites14. (The ‘poly- to Standard Mean Ocean Water (SMOW). A third sample, in contact mict’ modifier refers to the presence of olivine and pyroxene-rich with fusion crust, gave D17O 520.539%, d17O 5 3.09%,and lithic clasts among ureilitic clasts.) The sample has subrounded d18O 5 6.89% SMOW.